The invention relates generally to machines utilizing a tape head for laying composite tape on a surface.
In particular, the invention relates to tape laying machines where the tape laydown surface is contoured.
Composite tape laying machines are becoming well-known, especially in the aerospace industries. Such machines typically utilize a tape laying head which is movable on machine slides with respect to a mold or table laydown surface. As an example of the art, the tape head first dispenses parallel rows of composite tape and presses them to the laydown surface. Next the head may be rotated to form oriented plys of tape to build a laminated structure with anisotropic strength, where required.
The early form of tape laying machine dispensed composite tape plys to a flat mold surface to build up a part and, thereafter, the flat structure was then moved to a press to impart desired surface contours to the finished part. As tape laying art evolved, the capability for laying tape strips on contoured or shaped surfaces, as well as flat, was embodied in machine hardware and control functions. One popular style of machine utilizes a gantry or bridge which spans, and runs on, machine slideways which are held parallel to an elongate laydown surface. The tape head gantry also embodies means for driving the head transversely across the laydown surface and for swiveling the head so that angularly-biased plys can be laid. A tape head basically embodies a plate-like structure for supporting both a supply reel of composite tape and take-up reel for accumulating backing paper from the tape assembly as the tape is deposited on the laydown surface. The reels have horizontal axes and the tape is trained under a presser member. In one instance, the presser member might be a smooth shoe having line-contact transversely across the tape. In another instance, the presser member might be a cylindrical roller to compact the tape.
Several prior art references are illustrative of machine structure aimed at laying composite tape to a surface of changing contour, namely:
U.S. Pat. No. 3,574,040, Apr. 6, 1971 of B. E. Chitwood et al; PA0 U.K. Patent Appln. No. GB2,101,519A, published Jan. 19, 1983 of W. J. Murray et al; PA0 U.S. Pat. No. 4,461,669, July 24, 1984 of H. Dontscheff. PA0 U.S. Pat. No. 3,574,040, assigned to the General Dynamics Company, describes a traveling tape laying head wherein the entire head-tape reels, cutting assembly, and roller foot may be rotated around an axis lying along the tape laydown surface, by swiveling the assembly on an arcuate way system having a radius of curvature swung from the laydown surface. One disadvantage to the device is that the pressure roller is rigidly aligned with the tape head so that the entire head must be rapidly positioned in response to proximity sensors in order to adapt the pressure roller to surface contour changes. The large mass of the head may inhibit the speed with which the machine can adapt to contour changes.
U.K. Patent Appln. No. GB2,101,519A, assigned to the Vought Corporation, covers the so-called "Vought machine" or concept, which has been widely covered in trade publications covering the advanced composite tape laying machine developed by the Vought Corporation. Several articles include:
Jan. 24, 1983 issue of Desizn News. on pages 136 and 137, entitled "CNC Machine Slashes Composite Cost"; and October, 1984 issue of Machine and Tool Blue Book, pages 74-78, entitled "Automation Takes Aim At Composites Manufacturing".
Part of the Vought concept is to provide for an independent pivot motion of the tape laying shoe on the tape head. However, the shoe pivots around a pivot point located above the tape laydown surface, so that the shoe has a pendulum-type mounting--but is being pushed downward, from overhead weight. A pair of side potentiometers are affixed to the shoe and head to indicate relative motion as the lightweight shoe quickly adapts to contour changes. The sensed movement is fed back to a servodrive system to rotate the much heavier-weight tape head on an arcuate way system having a radius of curvature swung from the tape laydown surface.
One disadvantage to the Vought head and its shoe mounting arrangement is that, when the head descends to a contour surface which is not normal to the direction of descent, a corner of the shoe will immediately press the tacky tape to the laydown surface. Next, as the shoe pivots about the upper pivot pin, the shoe will slip across the tape surface to properly align with the contour surface. The tape, already stuck to the surface upon touchdown, is thereby starting to lay down out of position. This condition tends to be avoided if the shoe wobbles about an axis on the tape laydown surface.
Another feature of the Vought device is that counterbalance cylinders are used to control the downward force of the head, and are mounted on the pivotable head, so that the presser force is substantially normal to the contour. The head is split into a first section pivotable about the tape surface, and a second section which slides radially on the first section to allow for some "float" normal to the contour. While maintaining normal forces may be desirable, a disadvantage condition arises since the presser shoe can move radially from the point of zero radius established by the arcuate head track, so that the shoe may, in some instances slip from side-to-side on the tape as the head is pivoted.
U.S. Pat. No. 4,461,669, assigned to the Boeing Company, discloses a rudimentary design for a tape head which has the advantage of pivoting the presser foot about the tape laydown surface. The gist of the disclosure is that the lower presser member is pivoted on a plate which is attached to an upper control plate by a vertical parallel linkage framework, all carried on a tape head. By virtue of the parallel linkage therefor, as the control plate is pivoted, the presser member plate will also pivot, all rotation of the two being identical. Therefore, the pivot point of the control plate is manifested as a virtual pivot point on the presser member plate at the tape surface. However, certain disadvantages are seen in this mechanism, namely: while the disclosure refers to the Vought machine as requiring the entire mass of the head be pivoted on the machine ways, the parallel linkage mechanism similarly must pivot the masses of both tape reel assemblies as well as the cutter mechanism, all together with the presser plate. If these members are not all carried in pivotal relationship with the presser member, the tape would be trained from one reel to the other, intending to remain parallel to a plane parallel to the axes of the reels, while the pivoted presser member would impress on an outside edge of the tape, thus causing unequal stresses in the tape and a poor laydown condition. Another disadvantage of the system is that it may be difficult to practically manufacture and maintain the parallel link bars. Additionally, and unlike the Vought head, the force-directing pistons remain aimed at the original plane of the tape, so that when the presser member is swiveled, a vector component arises when applying a downward force with the pistons, so that the presser member and/or tape may tend to slide sideways along a sloped surface.
By way of clarification, it should be noted that while an extensive discussion of the Vought machine is embodied in the Background of the U.S. Pat. No. 4,461,669, the prior art schematic depicted in FIG. 7 of that patent does not, in fact, depict the pendulous pivoting shoe concept of the Vought machine, nor does the background of that invention mention the pivoting shoe of Vought. The prior art picture more closely resembles the General Dynamics machine wherein the presser member and tape head are rigidly tied to one another for unitary pivoting.
Applicant has obviated certain shortcomings inherent in the prior art devices by a construction wherein the presser member and tape head are concentrically rotatable around a point on the tape surface. The tape presser member has a circular way and follower system coupled to the tape head, and the tape head has a circular way and follower system coupled to the tape head carrier system. Sensor members detect initial rotation of the presser member in response to contour changes, and the sensor signal is utilized to effect a servodrive to move the tape head into alignment with the presser member. Thus, a rugged, reliable, and quickly adaptable system is provided to accommodate contour changes of the tape laydown surface.
The rotatable presser member is also provided with a brake to inhibit relative movement between the presser member and tape head at predetermined times, such as when the tape is being applied at an edge of a mold, and the presser member is not to rotate around or tip over the corner or a mold.
It is therefore, an object of the present invention, to provide for a presser member in a tape head system which is quickly adaptable to follow contour changes of a tape laydown surface.
Another object of the present invention is to provide for a relatively simple system for accommodating surface contour changes on a tape laydown surface, keeping the presser member normal to the tape surface.
Still another object of the present invention is to provide a tape laydown unit which will allow the tape presser member to freely follow contour changes of the tape laydown surface at selected intervals, and wherein the presser member may be braked, and thus not pivot, relative to the tape head at predetermined times.